1. Field of the Invention
The present invention relates to an electronic part and a method of fabricating thereof, in which the rise of a resin due to a capillary phenomenon is suppressed with respect to lead wires when a device connected to the lead wires is molded by a fluid resin thereon.
2. Description of the Related Art
In a light emitting diode (LED) display using a lead frame connected to an LED device, a stamping system is known as one example of the method of fabricating the lead frame. This system employs a method of fabricating a lead frame by using a die, wherein a lead frame having a predetermined pattern is fabricated by blanking a lead frame material by a progressive stamping die apparatus while the lead frame material is being consecutively transferred.
Thus, in the stamping system, since the lead frame material such as 42 alloy, SPCC, while being consecutively transferred, is blanked, burrs occur in front of the blanking direction. FIG. 13 is a schematic perspective view illustrating a state in which burrs have occurred in a lead frame which is used in an LED display. In FIG. 13, if a lead frame 1 is subjected to blanking in the direction of arrow X and in the direction of arrow Y, burrs 2 and 3 occur on the front side of the lead frame including leads 1 along the blanking direction.
Next, in a case where the LED device connected to the lead 1 of the lead frame is subjected to encapsulation by resin molding, the lead 1 of the lead frame on which the LED Chip is mounted is immersed in a liquefied (liquid state) epoxy resin, or a resin is applied to the LED Element mounted on the lead 1 of the lead frame by injection mold method or transfer mold method and hardened. At this juncture, the so-called resin climbing 5 occurs in which the resin rises from a resin liquid level designated by reference numeral 4 in FIG. 13, i.e., a surface of contact between the lead 1 of the lead frame and the fluid resin, up to the height H1 along the surface of the lead frame 1 owing to the capillary phenomenon.
When a resin coating is formed on a soldering effective portion of the lead frame 1 by the resin climbing 5, there are cases where when the lead 1 and outer leads or the like are electrically connected by soldering, faulty joining can occur, with the result that the LED device fails to operate with predetermined characteristics.
FIG. 14 is a perspective view illustrating an example in which a means is adopted for suppressing such resin climbing 5. In the example shown in FIG. 14, a pressing force is applied to the burrs 2 and 3, which occur in the lead 1 as shown in FIG. 13, from diagonal directions Z and W so as to squeeze the burrs 2 and 3, thereby forming coined portions 6 and 7. By providing such coining processing, the height of the resin climbing 5 of the resin is reduced to the height H2.
By providing coining processing for the burrs occurring in the lead frame as shown in FIG. 14, the height of the resin climbing 5 can be reduced. However, variations occur in the formation of the coined portions 6 and 7 at the time of coining processing. Further, since gaps Ga and Gb occur between each of the coined portions 6 and 7 and the flat surface portion, there has been a problem in that the rise of the resin due to the capillary phenomenon cannot be suppressed sufficiently.
The invention has been devised in view of the above-described problem, and its object is to provide an electronic part in which the resin climbing with respect to lead is suppressed when a device connected to the lead is encapsulated by a fluid resin thereon, thereby preventing the occurrence of faulty soldering.
In the invention, the above object of the invention can be attained by an electronic part in which a device is connected to a lead, and the device is encapsulated by a fluid resin thereon, characterized in that a groove for suppressing the rise of the resin is provided in the lead at a predetermined heightwise position from a surface of contact with the fluid resin. Namely the groove is located at near a boundary between a region of the lead to be mold and another region. In detail the groove is formed at a position apart from the boundary by a constant distance. According to this invention, by providing a groove for suppressing the rise of the resin in the lead at a predetermined heightwise position from a surface of contact with the fluid resin, resin climbing by a capillary phenomenon is suppressed to be able to prevent a solder-bonding from being caused by resin climbing.
In accordance with the above-described characteristic feature of the above structure of the invention, a groove for suppressing the rise of the resin is provided in the lead wire at a predetermined heightwise position from a surface of contact with the fluid resin when a device connected to the lead wire is encapsulated by casting a fluid resin thereon. For this reason, since the resin does not adhere to a portion of the lead wire located above the position of the groove, it is possible to prevent the occurrence of faulty soldering of an outer lead.
Preferably, the groove is formed to be perpendicular to the longitudinal(length) direction of the lead. In accordance with the above-described characteristic feature of the above structure of the invention, according to the groove perpendicular to the lead, resin climbing can be completely prevented to suppress a resin climbing confirmly.
Preferably, the groove is formed by stamping method so that the groove is formed on a face comprises a face facing to blanked surface.
Leads formed by stamping method are easy to generate burrs, and even if coining treatment for preventing burrs from being generated is conducted, resin climbing along a clearance easy to be generated.
In accordance with the above-described characteristic feature of the above structure of the invention, resin climbing can be completely prevented to suppress a resin climbing confirmly.
Preferably, the groove is formed by stamping method so that the groove is formed on a face comprises a face on which burrs are formed.
Preferably, the groove is formed on a face on which burrs are formed and the neighbor faces.
In accordance with the above-described characteristic feature of the above structure of the invention, resin climbing can be completely prevented to suppress a resin climbing confirmly.
Preferably, in the electronic part according to the present invention, a plurality of grooves are formed as the groove.
Preferably, in the electronic part according to the present invention, a projection is formed in such a manner as to be contiguous to the groove.
In accordance with the above-described characteristic feature of the invention according to claim 2, since a plurality of grooves are formed, even if the resin has leaked from the groove formed closest to the contact and has risen, the rise of the resin can be suppressed reliably by the ensuing grooves.
In accordance with the above-described characteristic feature of the invention, a projection is formed in such a manner as to be contiguous to the groove. For this reason, since both the groove and the projection serve as barriers for the rising resin, the resin climbing from the contact surface can be suppressed reliably by their synergistic effect.
According to this invention, the method comprises the steps of: preparing a lead frame having leads on which grooves are formed at a predetermined heightwise position from a region to be molded; mounting a chip on the lead frame; and molding the chip with a part of the lead so that the grooves are located outside of the molded region.
Preferable the step of preparing the lead frame comprises a step of forming at least outer leads located outside of the molding resin by stamping method.
In the case that at least outer leads are formed by stamping method, there is a problem that burrs are easy to be generated on the outer lead and resin climbing is easy to be caused. But according to the present invention, resin climbing can be prevented effectively.
Preferably the grooves are formed simultaneously on the step of forming lead frame by stamping method.
According to the method, reliable electronic parts can be obtained easily without increasing the process steps.
Preferably the step of molding comprises the steps of immersing the leads on which the chip is mounted and hardening the resin.
Preferably the step of molding comprises the steps of supplying a fluid resin into a recess of a case; and dipping the lead frame on which the chip is mounted into the a fluid resin.
According to the above method, resin climbing is suppressed to be able to prevent a solder-bonding from being caused by resin climbing.
Preferably the step of molding comprises the steps of: potting a resin onto the lead frame on which the chip is mounted; and hardening the resin.
Preferably the step of molding comprises the step of molding the lead frame on which the chip is mounted by transfer mold method.
According to the method, since melted resin pushed out from the die by pressure from inside of the die is stopped at the grooves, reliable electronic parts without burrs can be obtained. Even if resin burrs are generated, resin is embedded only within the grooves so as not to progress exceeding to the groves. Therefore only reliable electronic parts can be obtained without obstacle in appearance.